1. Field
Example embodiments of inventive concepts relate to injection-locked phase-locked loop (ILPLL) circuits, and more particularly, to ILPLL circuits using delay-locked loops (DLLs).
2. Description of Related Art
In a conventional source-synchronous system such as a dynamic random access memory (DRAM), an injection-locked phase-locked loop (ILPLL) is used to increase a correlation between a clock and data through a jitter tracking mechanism, and to reduce phase noise of a voltage-controlled oscillator (VCO).
However, since the lock failure of an ILPLL often depends on a phase of an injection signal, the phase of the injection signal must be locked without being affected by changes in process, voltage, temperature, etc.
For example, when a phase difference between an injection signal injected to the VCO of the ILPLL (e.g., an injection clock) and an output signal of the VCO of the ILPLL (e.g., an output clock) exceeds a maximum phase difference, in which an injection lock determined by a jitter tracking bandwidth required in a system, occurs, a number of frequency tones appear in the output clock of the VCO.